Designers, manufacturers, and users of electronic computers and computing systems require reliable and efficient equipment for storage and retrieval of information in digital form. Conventional storage systems, such as magnetic disk drives, are typically utilized for this purpose and are well known in the art. However, the amount of information that is digitally stored continually increases, and designers and manufacturers of magnetic recording media work to increase the storage capacity of magnetic disks.
In conventional magnetic disk data storage, the data is stored in a continuous magnetic thin film overlying a substantially rigid, non-magnetic disk. A magnetic recording layer that is a thin film of a magnetic alloy is formed on a disk. The recoding layer has a random mosaic of magnetic grains that behave as independent magnetic elements. Each bit of data is stored by magnetizing a small area of the thin magnetic film using a magnetic transducer (write head) that provides a sufficiently strong magnetic field to effect a selected alignment of the small area (magnetic grain) of the film. The magnetic moment, area, and location of the small area comprise a bit of binary information which must be precisely defined in order to allow a magnetic read head to retrieve the stored data/information. The disk may also include a soft magnetic underlayer that helps to concentrate the magnetic flux underneath the write pole of the head to increase the write field efficiency.
As technological improvements are made the areal data density of the disks increase. However, it is generally accepted that the conventional PMR film media has a maximum areal density between 500 Gbit/in2 to 1 Terabit/in2. In order to exceed this areal density limitation, various possible solutions are being developed including: Heat Assisted Magnetic Recording (HAMR), Microwave Assisted Magnetic Recording (MAMR) and bit-patterned media (BPM).
BPM is a promising technology that is likely to be commercialized in the next decade. Rather than a continuous magnetic recording layer film, BPM includes many small uniform magnetic “islands” or “dots” that are circular in shape and physically separated from each other on the disk media. The dots each include vertically oriented magnetic grains that are magnetically coupled together and behave like a large, single magnetic grain. Each of the magnetic dots constitutes a discrete magnetic domain or bit that is magnetized in a perpendicular or vertical manner to the disc either up or down. The magnetic dots are arranged in an array of circular tracks on the disk. FIG. 1 illustrates an exemplary recording disk 16 comprising an array of magnetic islands or dots 108. The bit pattern 50 includes a plurality of separate and discrete magnetic recording dots 52 organized into a staggered bit pattern. Each magnetic island or dots 108 is capable of storing a single bit of information. The areal density is increased because each bit of stored data corresponds to a pre-determined dot 108.
A potential problem with BPM is that magnetic moments at the edges of the magnetic dots can cause the dot to be unstable. This magnetization instability is noise that reduces the signal to noise ratio (SNR) of the dots and a low SNR increases the likelihood of disk malfunctions such as read or write errors. The magnetic instability at the edge of the dots is also one of the primary sources of media switching field distributions. What is needed is an improved magnetic element design that improves the stability of the magnetic dots.